The Hunley did not signal to shore with a blue lantern. The "blue light" which was mentioned twice in the historical record, once by Robert Flemming on the sunken Housatonic, and once by a postwar author, was not a blue lantern. In 1864, "blue light" referred to a pyrotechnic signal with a long history of use in the military and civilian sectors. Modern authors and researchers read "blue light" in the historical record and misinterpreted it as a blue oil-fired lantern, and the myth of the blue lantern has been repeated so often and for so long that it has achieved the status of gospel. The myth is wrong. Period dictionaries, military manuals, chemistry texts, popular published literature, etc all describe the use of pyrotechnic blue light. I have reproduced period blue light according to the formula in the US Ordnance Manual, and demonstrate its use in two YouTube videos: "Burning Blue Light" and "Making Civil War-Era Blue Light." You can check out the Wikepedia page for "Blue Light (pyrotechnic signal)" to get the true story; it is well referenced from primary sources, because I wrote it.